New PT question for Champ Clone

[surfsup]

I am trying to figure out PT selection for a tube rectified champ clone. Here is my thought process for PT choice based on the following layout:

[img1067]http://ceriatone.com/images/layoutPic/f ... Layout.jpg[/img]

There are four tubes as follows:

2 12ax7 preamp tubes will draw about 2-3mA each (figure 10mA for both)
1 6V6 power tube is max rated 5.5watts SE or 14watts PP (SE here since one PT)
1 5Y3 rectifier tube drop is 60V at 125mA

So the total current draw assuming worst case would be 10+6+125 = 141mA
The 5Y3 rectifier tube requires 5V and 2Amps on the heaters...

So looking at the Hammond PTs I'm looking for something close to 140mA with a 5V heater winding and at least 2A right?

http://www.hammondmfg.com/263.htm

I see these 4 possible choices:

270EX 118 115 60 550V C.T. @ 144ma. 5V @ 3A 6.3V @ 4A X9
272DX 123 115 60 600V C.T. @ 144ma. 5V @ 3A 6.3V @ 4A X9
274AX 137 117 50/60 720V C.T. @ 138ma. 5V @ 3A 6.3V C.T. @ 3.5A X10A
275X 167 115 60 800V C.T. @ 155ma. 5V C.T. @ 3A 6.3V C.T. @ 5A X11

The last three provide V that are getting up there (600-800V) so the 270EX is probably the first choice, then the 272DX would be my next best choice right?

But, I might want to use the 272DX as my primary choice? if I changed recto tubes later to something that required more amps, as per below:

I found this online:

5AR4/GZ34
GZ37 (3 amp filament current)
5V4G/A (Possibly lower if plate current of the power tubes is high enough)
5U4/G/A/B (3 amp filament current)
5R4G/A/B
5Y3G/B (what champ clone layout shows)

They're all interchangeable within limits. Every amp and each type of power tube has different limits so there are no general rules that apply universally.

All of these will "work" in the sockets intended for any of the other ones on this list.

Cautions: Most of these require 2 amps of filament current, the 2 exceptions are listed.

[ToneMerc]

I am trying to figure out PT selection for a tube rectified champ clone. Here is my thought process for PT choice based on the following layout:

[img1067]http://ceriatone.com/images/layoutPic/f ... Layout.jpg[/img]

There are four tubes as follows:

2 12ax7 preamp tubes will draw about 2-3mA each (figure 10mA for both)
1 6V6 power tube is max rated 5.5watts SE or 14watts PP (SE here since one PT)
1 5Y3 rectifier tube drop is 60V at 125mA

So the total current draw assuming worst case would be 10+6+125 = 141mA
The 5Y3 rectifier tube requires 5V and 2Amps on the heaters...

So looking at the Hammond PTs I'm looking for something close to 140mA with a 5V heater winding and at least 2A right?

http://www.hammondmfg.com/263.htm

I see these 4 possible choices:

270EX 118 115 60 550V C.T. @ 144ma. 5V @ 3A 6.3V @ 4A X9
272DX 123 115 60 600V C.T. @ 144ma. 5V @ 3A 6.3V @ 4A X9
274AX 137 117 50/60 720V C.T. @ 138ma. 5V @ 3A 6.3V C.T. @ 3.5A X10A
275X 167 115 60 800V C.T. @ 155ma. 5V C.T. @ 3A 6.3V C.T. @ 5A X11

The last three provide V that are getting up there (600-800V) so the 270EX is probably the first choice, then the 272DX would be my next best choice right?

But, I might want to use the 272DX as my primary choice? if I changed recto tubes later to something that required more amps, as per below:

I found this online:

5AR4/GZ34
GZ37 (3 amp filament current)
5V4G/A (Possibly lower if plate current of the power tubes is high enough)
5U4/G/A/B (3 amp filament current)
5R4G/A/B
5Y3G/B (what champ clone layout shows)

They're all interchangeable within limits. Every amp and each type of power tube has different limits so there are no general rules that apply universally.

All of these will "work" in the sockets intended for any of the other ones on this list.

Cautions: Most of these require 2 amps of filament current, the 2 exceptions are listed.

5Y3- 125mA is the current passing capacity, not it's draw. If all you are going to do is clone that circuit here's no need to reinvent the wheel, you can just do what Fender did, see drawing.

Here's an Edcor upright thats close to the Champ upright that I spec'd from Heyboer. It's current capability allows you to use just about any single power tube and the price is attractive too.

http://www.edcorusa.com/products/640-xpwr047_120.aspx



TM

[surfsup]

I am wondering if I am figuring out the PT correctly. Pretend I designed the ceriatone circuit but didn't pick a transformer yet. This is what I'm trying to understand, how to pick the proper transformer. Sorry if I was not clear.

On the edcor you posted, the secondary current is 120mA. I am trying to figure out what to look for. I understand the 5V and 2A for the heaters because the tube specifies that. I'm looking at Merlin's book now page 42...

[Firestorm]

The only current the rectifier tube requires from the PT is its heater current. 3A is plenty for any single tube you will use. It doesn't require current from the B+ supply; it makes the B+ supply.

So you have two 12AX7s which will typically use 2.5mA each, so your 10mA number is fine, with a nice margin of error in case you ever wanted to use 12AT7, 12AY7 or 12AU7.

At typical guitar amp voltages, a 6V6 will need less than 60mA plate and screen current, so a PT able to provide 70mA is right at the "entry level" for this type of amp. If you want the ability to use other output tubes, you would simply up the current rating of the PT you specify. At Champ voltages, a 6L6 might use something around 90mA, so your PT should be able to provide 100mA or so. The Edcor model ToneMerc suggested, would likely work with an EL34 or even a 6550 as well.

[surfsup]

Firestorm, thanks!

At typical guitar amp voltages, a 6V6 will need less than 60mA plate and screen current, so a PT able to provide 70mA is right at the "entry level" for this type of amp. If you want the ability to use other output tubes, you would simply up the current rating of the PT you specify. At Champ voltages, a 6L6 might use something around 90mA, so your PT should be able to provide 100mA or so. The Edcor model ToneMerc suggested, would likely work with an EL34 or even a 6550 as well.

That's great news for me as I have just decided to pull the EL34 out of a different amp and go with the original EL84 so this sounds interesting, a champ with an EL34 or 6V6 PT...

[Firestorm]

There will be some tonal impact of the OT's primary impedance with different tube types. If the OT has multiple secondary taps, you could adjust for the different types, but it shouldn't be "necessary." Don't use the cheapest OT you can find either; you want it to be able to handle the increased power of other tubes. Many original tweed Champ OTs (tiny, tiny things) will eventually blow just from 6V6s, but it takes 40 or 50 years before they die.

[ToneMerc]

Firestorm, thanks!

At typical guitar amp voltages, a 6V6 will need less than 60mA plate and screen current, so a PT able to provide 70mA is right at the "entry level" for this type of amp. If you want the ability to use other output tubes, you would simply up the current rating of the PT you specify. At Champ voltages, a 6L6 might use something around 90mA, so your PT should be able to provide 100mA or so. The Edcor model ToneMerc suggested, would likely work with an EL34 or even a 6550 as well.

That's great news for me as I have just decided to pull the EL34 out of a different amp and go with the original EL84 so this sounds interesting, a champ with an EL34 or 6V6 PT...

See the original thread, my last several posts.You are making this about 5X harder than it needs to be....lol

[Firestorm]

You are making this about 5X harder than it needs to be....lol

Yeah. If you really want to go to town, get Kevin O'Connor's third book. He tells you how to make a 60W Champ.

[surfsup]

I'm just trying to learn guys...

[Phil_S]

I'm having a tough time following this discussion today, so please excuse me if I rehash what's been covered.

You are overthinking this. It is very simple. There are three tubes in a Champ. Two of them use 6.3v filaments, and the 5Y3 used a 5v filament. This means you need 3 secondary windings, one for high voltage, one 6.3, and one 5V.

For filaments, the 12AX7 uses .3A and the 6V6 uses .45A. You need 6.3V @ ~1A. This allows a little extra for the pilot light, as .3 +.45 = .75. If forget what a #47 bulb needs, maybe .2mA.

The 5Y3 needs 2A. You need 5V @ 2A. That's your second winding.

Then you need to deal with the high voltage winding. A 6V6 requires about 45mA for SE use. One 12AX7 needs maybe 3mA. Call it 50mA for the HV secondary. Pick your poison for whatever high voltage you want -- typical gets about 340VDc on the plates -- with a true 5Y3, that is going to be around 310-0-310, +/-; that 320-0-320 shown is OK. Remember the Sovtek 5Y3 doesn't behave like a true 5Y3.

There you have it. The ones you are looking at have 2x the required mA on the HV winding and you will pay dearly for capacity you won't use.

Personally, I wouldn't bother with the tube rectifier for this amp. you can build a solid state rectifier for 50 cents and it's just as good or better. Others will argue it isin't, and everyone is certainly entitled to their opinion. Thiis allows you to get a PT without the 5V winding, and that will save you some money, too.

I don't know what sort of cost your are looking at, but the 325-0-325 you see here will do the job at a very good price: http://www.musicalpowersupplies.com/4.html

Tube data sheets are here: http://tubedata.itchurch.org/index.html
Bookmark this link. All the answers to your question are taken from the data sheets.

[surfsup]

Phil i see i totally screwed up and added in the max wattage for the 6v6 instead of the current draw, but with the 125 mA of the recto i was way off anyway. Your post is great thanks. Mainly i was wondering how the recto affected things.

Thanks so much!

If recto tubes suck, why use them? The TW rocket i think i will build uses one as well if memory serves...

[martin manning]

A #47 pilot lamp draws 150mA. People like tube rectifiers for the voltage sag with increased current draw. Other people say that you can get exactly the same effect with a resistor.

[Phil_S]

A #47 pilot lamp draws 150mA. People like tube rectifiers for the voltage sag with increased current draw. Other people say that you can get exactly the same effect with a resistor.

Thanks, Martin. By bad...I wrote ".2mA" when I meant .2A. In my mind, I was pretty close.

[Phil_S]

If recto tubes suck, why use them?

They don't suck, the just suck voltage and current! What I really think is, some players get really good at milking the sag you can get from a tube. If it's part of your sound, by all means, use tubes. It's all about sag and whether you can control it and use it. I'm not against tube rectifiers, I just think, on a dollar/performance basis, they are on the expensive side. Then, if you don't use the sag, it hasn't much value. That's all.

BTW, for the record, I have at least half a dozen amps with tube rectifiers.

[surfsup]

"I have at least half a dozen amps with tube rectifiers"



I have some amps to build!!!